1. Field of the Invention
The present invention relates to a radar transponder which, on reception of a high frequency signal such as a microwave signal from a radar, responds to (synchronize with) the signal and transmits a high frequency response signal.
2. Description of the Prior Art
FIG. 1 is a circuit block diagram of a conventional radar transponder. In FIG. 1, reference numeral 1 is a receiving antenna, 2 a direct diode detector, 3 a video amplifier, 4 a control circuit, 5 a transmission gate circuit, 6 a sweep signal generator, 7 a microwave oscillator, and 8 a transmitting antenna.
FIG. 2 is a perspective view showing a conventional radar transponder. In FIG. 2, reference numeral 9 is a receiving unit which receives a microwave signal (a high frequency signal) from a radar not shown in the diagram, 10 a transmitting unit which transmits a response signal in response to the received high frequency signal received by the receiving unit 9, 11 a printed-circuit board for a power source circuit, 12 a printed circuit board for a signal control circuit, 13 a printed circuit board for a video amplifier, 14 a printed circuit board for a lamp . LED indication circuit, and 15 wirings for connection with each printed circuit board. The above-mentioned printed circuit boards are all ordinary rigid printed circuit boards.
Next, the operation will be described. A microwave signal received by the receiving antenna 1 coming from a radar is detected by the direct diode detector 2, the detected output is amplified by the video amplifier 3, and is sent to the control circuit 4. The control circuit 4 forms pulses for creating the transmission time of a radar transponder using an input video amplified signal and transfers the pulses to the transmission gate circuit 5. The transmission gate circuit 5 forms transmission gate pulses using the transferred output pulses from the control circuit, and the transmission gate pulses are input to the sweep signal generator 6 and the microwave oscillator 7. The sweep signal generator 6 generates saw-tooth voltage which wave form consists of a required number of saw-tooth pulses using the transmission gate pulses and transfers them to the microwave oscillator 7. The microwave oscillator 7 performs transmission for a fixed time set by the transmission gate pulses and performs frequency sweep in a regular frequency range using the saw-tooth output voltage. A frequency swept signal from the microwave oscillator 7 is propagated into the space by the transmitting antenna 8.
Since the conventional radar transponder had its receiving wave detecting portion which was only a direct diode detector composed of only detecting diodes as described above, there was a problem that the limit of the minimum receiving sensitivity of the conventional radar transponder was -45 dBm or so.
Furthermore, it was necessary to connect each printed circuit board using wires, and soldering work and wire assembly involved much labor.
Moreover, there was a problem that radar transponders did not normally operate owing to forgotten wirings or wrong wirings.